The penetration length of Infrared light for silicon (Si) is long. Thus, in manufacturing a supersensitive sensor which utilizes near infrared light, a long optical length needs to be formed within silicon. Moreover, photoelectric conversion occurs at a deep position from the silicon surface corresponding to light entrance plane; therefore, a potential for storing electrons needs to be formed at a deep position.
For forming a potential at a deep position, ultra-high energy ion-implantation (ion implantation) is needed according to conventional methods. In this case, development cost and manufacturing cost considerably increase depending on situations. In addition, development of a suitable resist is also demanded, and thus the level of difficult development may further increase.
For overcoming this problem, a method has been developed where ion is implanted from both a front surface and a rear surface of a silicon substrate to form photo diodes located at a deep position and capable of storing sufficient electrons obtained by photoelectric conversion of infrared light (i.e., a method not requiring ultra-high energy ion implantation) (for example, see Patent Document 1).
According to this method, ion is initially implanted from the front surface of the silicon substrate to form a photo diode in the surface of the silicon substrate at a depth equivalent to the depth of an image sensor handling visible light. Then, the silicon substrate is turned over to polish the rear surface of the silicon substrate. Thereafter, ion is implanted from the rear surface of the substrate to form a photo diode at a depth equivalent to the depth of the image sensor handling visible light. This manufacturing method forms a photoelectric conversion area having a doubled depth at the maximum in the depth direction without the necessity of ultra-high energy ion implantation.
The turned over silicon substrate is polished to a necessary film thickness. After ion implantation, the polished silicon substrate is joined with a support substrate for supporting the thickness of the silicon after the polishing. Then, an impurity having been ion-implanted from the rear surface of the silicon substrate is activated by high-temperature activation processing.